Governor Don Carcieri signed a law making Rhode Island the first state to require cat owners to spay or neuter their pets.
Cat owners must spay or neuter pets older than six months unless they pay $100 for a breeder's license. Violators can be fined $75 per month.
"By signing this legislation today, we are taking the necessary steps to reduce the number of impounded cats that are euthanized in cities and towns throughout the state," Carcieri said in a written statement.
The law would also save money by cutting down on housing and feeding costs at city shelters, he added.
Private shelters and municipal pounds in Rhode Island killed about 1,600 strays in 2004, the most current figure available, according to the state Department of Environmental Management.
Some animal-rights advocates worried that the bill could lead cat owners to abandon their pets rather than risk a fine or pay for the procedures.
Under the law, low-income pet owners would be eligible for subsidies for low-cost surgery.
Farmers are exempt.